Sweetbreads Off Menu in Mad Cow Fears : Britain: Authorities ban the delicacy because a new study suggests that it could be infected with the ailment.

There’s plenty of beef but no more sweetbreads on the menu at Le Gavroche, a chic French restaurant here.

No use going elsewhere. You won’t find home-grown sweetbreads, made from calves’ thymus, on any menu in Britain.

The government has banned foods containing intestine or thymus from calves because a new scientific study suggested that they might be contaminated with the infectious agent of bovine spongiform encephalopathy, commonly called “mad cow disease.”

The sweetbread alert, in addition to recent threats by Germany to stop British beef imports, has focused new attention on the fatal brain ailment that has killed 131,050 cattle in the last eight years.

The government insists that beef is safe, particularly because all infected cows are killed and not used for food.

Taking a similarly cautious approach, the European Union’s agriculture commissioner, Rene Steichen, recently proposed banning exports of carcasses from British herds that had not been disease-free for at least six years.

Steichen’s spokesman, Gerry Kiely, said there was no evidence that mad cow disease threatened humans. “We’re taking measures to exclude a risk which is not there by all evidence,” he said in Brussels.

British government investigators who did the recent study said it sheds light on the basic biology of the illness--showing how the agent travels through the cow’s body--but does not prove that the thymus or intestine are dangerous to eat. The ban was taken as a precaution.

“There is no evidence that even if you ate infected brains you’d get BSE (mad cow disease), but the government has to be cautious,” said Kevin Taylor, assistant chief veterinary officer of the Ministry of Agriculture, Fisheries and Food.

The epidemic has spurred scientific studies exploring the basic biology of both the human and animal forms of this puzzling ailment.

“It’s a red-hot area of science,” said Dr. Gareth Roberts, a neuroscientist at Harrow Hospital. “We’ve learned a lot more about the molecular biology of the disease.”

Spongiform encephalopathy is a fatal brain disease striking animals and humans, causing sponge-like holes in the brain. Cattle with the disease stagger and drool, symptoms giving the disease its popular name.

No one knows what causes the ailment, which can linger for 30 years in humans or five years in cows before symptoms strike.

Cows are thought to have caught the disease by eating offal from infected sheep, which has since been removed from their food supply.

The human forms of the disease, all extremely rare, are called kuru, Creutzfeld-Jakob Disease (CJD), and German-Straussler Scheinker Syndrome (GSS). It strikes less than one in a million people worldwide.

People in Papua New Guinea got kuru from eating infected human brains.

About seven American children and a few in Britain, France and Australia got CJD when they were treated with human growth hormone derived from brain tissue between 1963 and 1985. Shortly after the link was identified in 1985, most countries banned the use of brain-derived human growth hormone and switched to genetically synthesized hormone.

Some people get it from inheriting a faulty brain protein.

There is no evidence that anyone has ever gotten the disease from eating beef from an infected cow. In fact, the human and animal forms may be triggered by different agents.

Despite a slew of studies, no one knows the specific agent that provokes the brain damage.

The mysterious agent alters the shape of a crucial brain protein, progressively destroying the brain, said Professor John Bourne, director of the Institute for Animal Health.

Some scientists suspect the agent is a virus-like substance; others say it is an infectious protein.

The new British study offers a glimpse into the basic biology of the illness by showing that it somehow travels through the intestine before getting to the brain.

Government scientists infected 4-month-old calves with BSE by feeding them brain stems from sick cows. The calves were then killed two months, six months or 10 months later.

Scientists injected a variety of cow parts into the brains of mice. Those that were injected with pieces of small intestine contracted spongiform encephalopathy, suggesting the infectious agent lurks in the gut.

Although the study did not provide evidence that the disease is in the thymus, the government officials banned its use for sweetbreads as a precaution.